The invention relates to an apparatus for the conveyance of collected debris or screenings on a bar screen partially immersed in a sewage flow and inclined in the direction of flow, in certain cases with an adjoining apron screen, to a discharge position situated at an upper edge of the bar screen or the apron screen, with the aid of a rake device periodically movable between the bars of the bar screen, by means of which the screenings are heaped together periodically along a conveyance path.
Such an apparatus serves for the removal and conveyance from the sewage of screenings adhering to the bar screen by being guided periodically along a conveying path from the bottom upwardly by a rake device. The overall length of the conveying path is determined by the length of the bar screen and by the length of the adjoining apron screen, wherein applicable.
In a known rake device according to DE-PS 16 58 096 (corresponding to U.S. Pat. No. 3,591,006) the drive period of the rake determined by the length of the conveying path and the speed of conveyance. Since the speed of conveyance cannot be increased beyond a given value, the drive period becomes very great particularly with long conveying paths. This leads to an increase in the amount of screenings which become collected on the bar screen within the drive period and which have to be conveyed.
Excessively large quantities of screenings collected on the bar screen can partly block the latter, so that the necessary hydraulic flow no longer is guaranteed. At maximum hydraulic load maximum quantities of screenings also frequently occur, and blocking of the bar screen by screenings can cause critical operating conditions. Moreover, unblocking of the bar screen, and where applicable the adjoining apron screen, in a single movement of the rake device requires considerable structural outlay with respect to the rake operating mechanism and necessitates a free extension height above the discharge position. This can be achieved only with a corresponding increase in height of the building or structure housing the screen and hence by an uneconomical site expenditure.